1. Field of the Invention
The present invention relates to a chemically amplified resist composition, and, more particularly, to a chemically amplified resist composition suitable for super-fine works using radiations, such as ultraviolet rays, deep ultraviolet rays, X-rays, and charged particle rays.
2. Description of the Background Art
There is an increasing demand for miniaturization of processing sizes in lithography in the fields requiring fine works such as manufacture of semiconductor devices or integrated circuits (ICs) in order to achieve high integrity in ICs. Technologies capable of processing fine works even of a size of 0.5 .mu.m or smaller in a stable manner are required in recent years. Because of this, resists used in such a technology must have capability of forming patterns with a size smaller than 0.5 .mu.m at a high precision. Lithographic techniques using radiations with a shorter wavelength are also being studied.
Included in such radiations are ultraviolet rays (e.g. i-line (365 nm)), deep ultraviolet rays (e.g. KrF excimer laser (248 nm)), X-rays (e.g. synchrotron radiation), and charged particle rays (e.g. electron beam). A number of resists to which these radiations can be applied have been proposed in recent years.
Among such resists, of particular interest are those of which the rate of dissolution in a developer can be changed by an acid produced by irradiation. This kind of resists is generally called "chemically amplified resists" (Chemically Amplified Resists, A. A. Lamola, et al., Lithography Materials & Processing, 53-60, 34, No. 8, (1991)).
In the manufacture of ICs using a chemically amplified resist, a resist solution is first prepared. Typically, this resist solution comprises (a) a resin protected by a group decomposable by an acid (hereinafter referred to as "acid-decomposable protective group"), which is converted into an alkali-soluble resin when the acid-decomposable protective group is decomposed (such a protected resin is more specifically defined hereinafter and referred to as "blocked resin"), (b) a compound which generates an acid by irradiation (hereinafter referred to as "photoacid generator"), and (c) a solvent which dissolves the blocked resin and the photoacid generator. This resist solution is then applied to a substrate by using a spin coater or a roll coater to form a resist coating. Adequate coatability and storage stability are thus essential characteristics for the resist solutions in order to enable sophisticated fine works to be constantly implemented. Irradiation to the resist coating produces patterns suitable for fine works. The shape of the patterns greatly affects the precision of the fine works, and a rectangular pattern is considered to be a preferred pattern.
Ethylene glycol monoethylether acetate and the like are known as solvents used for the preparation of a conventional lithographic resist solution comprising a novolak resin and a naphthoquinone diazide compound as a photosensitizer. The use of ethylene glycol monoethylether acetate as a solvent for preparing a solution of a chemically amplified resist poses a problem of storage instability. Depending on the period of time for which the resist solution prepared from this solvent has been stored, there may occur unevenness in the resist coating sensitivity, resulting in irregular patterns.
Further, along with the requirements for high integrity of ICs in recent years, substrates (silicone wafers) with a larger diameter, e.g., 4 inch, 6 inch, or even 8 inch, are employed in order to increase the yield and to promote the efficiency in the manufacture of ICs. A solution of chemically amplified resist prepared using ethylene glycol monoethylether acetate as a solvent exhibits only inadequate spin-coatability on such large diameter substrates.
An object of the present invention is therefore to provide a novel composition for chemically amplified resist which exhibits superior sensitivity and resolution capability and can be excellently applied especially to large sized substrates by spincoating.
Another object of the present invention is to provide a composition for chemically amplified resist which exhibits excellent storage stability and forms resist coating for producing excellently shaped patterns, thereby ensuring fine works to be constantly implemented.
Still another object of the present invention is to provide a composition for chemically amplified resist having superior storage stability, which can exhibit high sensitivity and produce excellently shaped patterns with good reproducibility even after storage for a long period of time.
The present inventors have undertaken extensive studies, and found that the use of specific kinds of solvents in combination with (a-1) a blocked resin, (a-2) a combination of an alkali-soluble resin and a dissolution controlling agents (hereinafter defined), or (a-3) a combination of an alkali-soluble resin and a crosslinking agent, and (b) a photoacid generator can achieve the above objects.
The present inventors have further found that the following solvents can be excellently used as said specific kinds of solvents for chemically amplified resist compositions of negative-tone type and of positive-tone type.
(1) Solvents used for negative-tone type amplified resist compositions:
(i) an ester of a saturated carboxylic acid having 1-4 carbon atoms with no substituent and an alcohol having 1-6 carbon atoms (hereinafter referred to as "ester solvent"),
(ii) a mixture of ester solvent (i) and an alkyl lactate, or
(iii) a mixture of an alkyl lactate, a propylene glycol alkyl ether and/or a propylene glycol alkyl ether acetate.
(2) Solvents used for positive-tone type amplified resist compositions:
(i) the ester solvent,
(ii) a mixture of ester solvent (i) and an alkyl lactate,
(iii) a mixture of an alkyl lactate, a propylene glycol alkyl ether and/or a propylene glycol alkyl ether acetate, or
(iv) a propylene glycol alkyl ether acetate.